In the field of power generation, a significant amount of electricity is generated by burning of fossil fuels and especially coal.
One of the major problems associated with burning coal is the issue related to inorganic materials in the coal. Coal after combustion can leave amounts of ash of as high as 10 weight percent. The ash is essentially inorganic matter. The inorganic matter causes problems in slagging and fouling of the furnaces; see for example, the teachings of U.S. Pat. Nos. 4,372,227 and 5,894,806; and U.S. patent publication No. 2004/022928. Slagging is defined as the deposition of fly ash on the heat transfer and refractory surfaces in the furnace volume that is subjected to radiant heat transfer. Fouling is defined as a deposition in the heat recovery section of the steam generator mainly due to convective heat exchange by fly ash quenched to a temperature below its melting point. Compounds, mainly inorganic, that have vaporized in the combustion zone can and will condense on the heat transfer surfaces by condensation of the volatiles or by the sulphation of SO3 which is formed by oxidation of the sulfur components in coal. Depending on the amount of deposition, they can significantly impact the efficiency of the furnace. Besides the combustion conditions, the deposits formed depend mainly on the release and chemistry of the chlorine, sulphur, aluminum silicates and alkali metals during combustion. Various solutions to the issue have been proposed; see for example, the teachings of U.S. Pat. Nos. 4,057,398 and 4,372,227; and patent publication Nos. 2004/022928, 2008/0271657, and 2009/0178599. However, controlling and reducing the deposits which cause slagging and fouling remains a major issue in efficient operation of coal fired plants.
Consequentially, the continued use of coal in this manner is becoming increasingly complicated as more stringent environmental rules and regulations with respect to sulphur emissions, heavy metal disposal and carbon footprint are implemented.